This invention relates to polymers prepared from cyclobutarene monomers, and processes for preparing them. Historically, one specie of this genus has been called benzocyclobutenes, but they are more properly named benzocyclobutanes, and will be called such in this document. The Chemical Abstract Service registry name is bicyclo(4.2.0)octa-1,3,5-triene.
Thermoset resins are compositions which solidify irreversibly upon curing. Such resins are useful in many engineering applications such as coatings, structural laminates, adhesives, films, and composites. Desirable physical properties include enhanced chemical resistance, high tensile strength, high temperature resistance, electroinsulative properties, and oxidative stability.
Many aerospace manufacturers require that composite materials retain greater than 50-60 percent of their strength at 325.degree. F. after exposure to boiling water for prolonged time periods.
Bismaleimides are commercially available monomers currently being evaluated as a potential matrix resin for high performance structural composites where excellent thermal and thermooxidative stability are required. Unfortunately, polymaleimide homopolyers are susceptible to degradation of their physical properties by moisture as well as many common organic solvent. Polymaleimides have good thermal stability but are extremely brittle indicating that these thermoset resins have a high degree of crosslinking. In an attempt to solve this problem, a second component is sometimes added, usually an aromatic molecule with either an allyl or propenyl substituent. While these polymers have improved toughness over the bismaleimide homopolymers, they do not show any decreased water absorption.
It would be desirable to have new thermoset polymers with improved properties or improved combinations of properties compared to those of polymaleimide homopolymers. Some of these properties include decreased water absorption, enhanced solvent resistance, and a high glass transition temperature. It would be further desirable to prepare such polymers at temperatures lower than about 200.degree. C.